Fix for order by limit for sys tables (ydb-platform#28224)

Author: XJIE6

ydb/core/kqp/ut/olap/sys_view_ut.cpp

@@ -633,6 +633,17 @@ Y_UNIT_TEST_SUITE(KqpOlapSysView) {
 
         auto tableClient = kikimr.GetTableClient();
 
+        {
+            auto selectQuery = TString(R"(
+                SELECT *
+                FROM `/Root/olapStore/.sys/store_primary_index_stats`
+                ORDER BY PathId
+                LIMIT 10
+            )");
+
+            auto rows = ExecuteScanQuery(tableClient, selectQuery);
+        }
+
         {
             auto selectQuery = TString(R"(
                 SELECT *

ydb/core/tx/columnshard/engines/metadata_accessor.h

@@ -24,16 +24,17 @@ class ITableMetadataAccessor {
 
 public:
     ITableMetadataAccessor(const TString& tablePath);
+
+    virtual bool OrderByLimitAllowed() const {
+        return true;
+    }
     virtual bool NeedDuplicateFiltering() const {
         return true;
     }
     virtual bool NeedStalenessChecker() const {
         return true;
     }
     virtual ~ITableMetadataAccessor() = default;
-    virtual TString GetOverridenScanType(const TString& defScanType) const {
-        return defScanType;
-    }
     virtual std::optional<NColumnShard::TUnifiedOptionalPathId> GetPathId() const {
         return std::nullopt;
     }

ydb/core/tx/columnshard/engines/reader/common_reader/constructor/read_metadata.h

@@ -25,7 +25,7 @@ class ISourcesConstructor {
     virtual TString DoDebugString() const = 0;
     bool InitCursorFlag = false;
     virtual void DoFillReadStats(TReadStats& /*stats*/) const {
-    
+
     }
 
 public:
@@ -192,6 +192,10 @@ class TReadMetadata: public TReadMetadataBase {
     TReadMetadata(const TReadMetadata&) = delete;
     TReadMetadata& operator=(const TReadMetadata&) = delete;
 
+    bool OrderByLimitAllowed() const {
+        return TableMetadataAccessor->OrderByLimitAllowed() && !GetFakeSort();
+    }
+
     virtual std::vector<TNameTypeInfo> GetKeyYqlSchema() const override {
         return GetResultSchema()->GetIndexInfo().GetPrimaryKeyColumns();
     }

ydb/core/tx/columnshard/engines/reader/simple_reader/iterator/scanner.cpp

@@ -29,7 +29,7 @@ TScanHead::TScanHead(std::unique_ptr<NCommon::ISourcesConstructor>&& sourcesCons
         SyncPoints.emplace_back(std::make_shared<TSyncPointResultsAggregationControl>(
             SourcesCollection, Context->GetSourcesAggregationScript(), Context->GetRestoreResultScript(), SyncPoints.size(), context));
     } else if (readMetadataContext->IsSorted()) {
-        if (readMetadataContext->HasLimit() && !readMetadataContext->GetFakeSort()) {
+        if (readMetadataContext->HasLimit() && readMetadataContext->OrderByLimitAllowed()) {
             auto collection = std::make_shared<TScanWithLimitCollection>(Context, std::move(sourcesConstructor));
             SourcesCollection = collection;
             SyncPoints.emplace_back(std::make_shared<TSyncPointLimitControl>(

ydb/core/tx/columnshard/engines/reader/simple_reader/iterator/sys_view/abstract/metadata.h

@@ -24,8 +24,8 @@ class TAccessor: public ITableMetadataAccessor {
         return PathId;
     }
 
-    virtual TString GetOverridenScanType(const TString& /*defScanType*/) const override {
-        return "SIMPLE";
+    virtual bool OrderByLimitAllowed() const override {
+        return false;
     }
 
     virtual bool NeedDuplicateFiltering() const override {

ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.cpp

@@ -109,7 +109,7 @@ void TTxScan::Complete(const TActorContext& ctx) {
                 return request.GetCSScanPolicy() ? request.GetCSScanPolicy() : defaultReader;
             }();
             auto constructor =
-                NReader::IScannerConstructor::TFactory::MakeHolder(read.TableMetadataAccessor->GetOverridenScanType(scanType), context);
+                NReader::IScannerConstructor::TFactory::MakeHolder(scanType, context);
             if (!constructor) {
                 return std::unique_ptr<IScannerConstructor>();
             }